UStepper Robot Arm

This instructable takes you through the process of building your own cool robot arm!

The Robotic Arm is developed entirely by me, the nut covers are however, from a guy on thingiverse. All STL files are avilable for you to print (for personal use - not for selling!) on our GitHub.

So let's get to it!

First you will need some parts. Besides the 3D printed parts, which I will introduce in the next section, you will need bearings, nuts and bolts. I have spent some time on reducing the number of unique items on the BOM, but there is still a few.

Bolts:

• 1 pc. M8 x 40 mm
• 1 pc. M8 x 70 mm
• 4 pcs. M4 x 20 mm
• 4 pcs. M4 x 35 mm
• 20 pcs. M3 x 10 mm
• 3 pcs. M3 x 16 mm
• 10 pcs. M3 x 20 mm
• 9 pcs. M3 x 25 mm

Nuts:

• 21 pcs. M3
• 8 pcs. M3 self locking
• 8 pcs. M4 self locking
• 2 pcs. M8 self locking

Washers:

• 2 pcs. M8, OD: ~15.8 mm
• 2 pcs. M4, OD: ~8.8 mm

Bearings:

• 4 pcs. 608Z
• 12 pcs. 624Z

Rods:

Aluminium rods, the diameter is outer diameter, they are of 1 mm material, making the inner diameter of the 15 mm rods = 13 mm. I found these rod sizes (diameters) in the local hardware store.

• 1 pc. 15 x 200 mm
• 1 pc. 15 x 150 mm
• 2 pc. 6 x 170 mm
• 1 pc. 6 x 165 mm

Additional items:

• Super glue
• Micro servo
• 3 pcs. NEMA 17 stepper motor
• 3 pcs. uStepper control boards (optional)

Tools:

• Adjustable wrench
• Hex Keys (if you use hex bolts like I did)
• Philips screwdriver

Now for the 3D printed parts. First of all, I printed all of them in PLA. The infill was set to 25% for all parts, besides the three motor gears which are printed with 100% infill. The numbers on the parts will be used in the assembly instructions given in the following section. All STL files are available on our GitHub for personal use.

Just follow the instructions in the pictures here. The only thing to notice is that the motor gears has changed since I took these pictures. This was done to make them more robust, and get a better grip on the motor.

For the robot arm to run, you will need some stepper driver. I recommend uStepper, but there are plenty of other solutions out there. What I go through here is based on the uStepper setup.

The three uSteppers are connected as shown here on the diagram. One uStepper is master, receiving data through the UART and distributing this to the two slaves.

To make it easy, I used a prototype shield on the master so that I could easily connect bluetooth module, servo and slaves.

If using USB cable for communication, it is essential that it is secured properly to avoid breaking the USB on the uStepper when rotating the arm.

Programming the arm is relatively easy, since I have already made a working sketch :) The sketch is based on a teach mode operation principle. That is, you move the robot arm around and record positions, which you then play back. The code setup is shown in the video below, and the code is found on our GitHub.

In the video, you can also see how to interface with the Robot Arm using the example code.

The code does not make closed loop movements, but this is possible with the new uStepper library, by adding the PID in setup like shown in the video:

That is pretty much it! All the rod lengths can be adjusted to give the robot arm a different range than that shown in this instructable.

As it is now, no inverse kinematics has been implemented, but we are working on it together with a suitable protocol between master and slaves.

More information about uStepper and the Robot Arm can be found on www.ustepper.com